take hold of the handles, and pull them apart as if you were going to blow."

Nathan did so. He pulled the handles apart, and held them open.

"Now," said Jonas, "I will stop up the nose, and the valve will close itself; and then you will find that you cannot bring the sides together again."

So Jonas put his thumb over the hole, and told Nathan to blow.

Nathan pressed hard, and the sides came together again, about as easily as usual.

"What!" exclaimed Jonas with surprise. He did not know what to make of the failure of his experiment.

"There must be a leak somewhere," said he. And he took the bellows out of Nathan's hand to look for it.

He found there was a corner, on the side opposite to the one where he had been working, where the leather was open, he having forgotten to nail it down.

"Ah!" said he, "here is the difficulty. When I have nailed this down, we will try again."

"Is that a leak?" said Nathan.

"Yes," said Jonas. "When you worked the bellows, you pressed the air all out through there. I did not know that that was open. Let me nail this down, and then we will begin our experiment regularly."

QUESTIONS.

What was Jonas doing in the shop, when Rollo and Nathan went out to find him? What part of the bellows was out of order? How did he make a new valve? How did he fasten it to its place? Did he nail down only one edge, or both edges? Why did he want the other edge to be left at liberty? How did he prevent its lifting up too far? What was the first experiment which he performed with the bellows, after he had finished the mending? Did it succeed at first? Why not? In working a pair of bellows, where does the air come in? Where does it go out? Why cannot the air escape through the valve where it comes in?

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CHAPTER IV.
EXPERIMENTS.

When Jonas had finished nailing down the corner, he said, "Now there are several experiments, which we can perform with the bellows. I will be the professor, and you two shall be my class in philosophy, and I will direct you how to make the experiments.

"First," said Jonas, "you, Rollo, may take hold of the nose of the bellows with your hand, in such a way as to put your thumb over the end of it, to stop it up, and then let Nathan try to blow."

Rollo did so, and Nathan tried to blow. He found that he could open the bellows very easily; but when he attempted to press the sides together again, he could not. He crowded the handle belonging to the upper side down, as hard as he could, but it would not move.

"What makes it do so?" said Nathan.

"The air inside," said Jonas. "We have stopped up all the places, where it could get out. The valve stops itself. Rollo stops the nose with his thumb, and I have nailed the leather down close, about all the sides. And so the air can't get out, and that keeps you from bringing the sides together again."

Nathan tried again with all his strength. The sides came together very slowly.

"They're coming," said he.

"Yes," said Jonas. "They come a little, just as fast as the air can leak out through the little leaks all around."

"I thought you stopped all the leaks," said Nathan.

"Yes," replied Jonas, "I stopped all the real leaks, but still I can't make it perfectly tight. Some air can escape between the leather and the nails all around, and just as fast as it can get out, so fast you can press the sides together, and no faster."

Here Nathan tried again with all his strength; but he could only bring the sides together very slowly.

"Now comes the second experiment," said Jonas. "While Nathan is trying to press the two handles together, you, Rollo, may run your finger into the hole, and push up the valve a little."

Rollo did so. He pushed up the valve a little with his finger, and that allowed the air to escape through the opening. The consequence was, that the bellows collapsed at once under the pressure which Nathan was exerting upon them.

"There," said Jonas, "you see that when the air is kept in, you cannot bring the sides together; but when I let the air out, then they come together easily."

"Yes," said Nathan; "do it again, Rollo."

So they performed the experiment again. Nathan pulled the handles apart wide, while Rollo kept his thumb over the nose, to keep the air from issuing through. Then Nathan tried to press them together; but he could not, until Rollo put his finger under, and pushed up the valve a little, and then they came together again very easily.

"The air is a real thing, I verily believe," said Nathan.

"Yes," said Rollo, "I know it is. And now for the third experiment, Jonas."

"The third experiment," said Jonas, "is this. Turn the bellows bottom upwards, and try to blow."

Nathan did so. He found that he could work the bellows easily—too easily, in fact; but they did not blow.

"Hold your hand opposite the nose, and see if any wind comes," said Jonas.

They did so; there was no wind, or rather scarcely any.

"The reason is," said Jonas, "that, when the bellows are bottom upwards, the valve hangs down off from the hole all the time, and lets the air all out through the hole in the side; and it can come out more easily there than through the nose, and so it don't blow well."

"Well, Jonas," said Rollo, "that's a pretty good experiment; but what is the next? Let me try the next. Nathan, it is my turn."

"The next experiment, which is the fifth,——"

"No, the fourth," said Nathan.

"The fourth, then," said Jonas, "is to prove what I said to you—that the air, which is blown out at the nose of the bellows, really comes in through the valve. Let me see,—I want something to make a smoke."

"Will not paper do?" said Rollo.

"Yes," said Jonas, "here is some brown paper, which will do." So Jonas rolled it up, and told Rollo to set it on fire, and then, when it was well burning, to step on it with his foot, and put the flame out.

Rollo did so, and the paper lay in a heap, making a great smoke upon the hearth, just before the fire.

"Now," said Jonas, "put the bellows upon its edge, by the side of the paper, so as to have the valve near the smoke, and then hold still a minute, until the smoke comes up steadily by the valve."

When this was done, Jonas told Nathan to take hold of the nose of the bellows, to steady it, so that Rollo could blow. He then directed Rollo to lean the bellows over a little towards the smoke, so that the moving side should not rub upon the hearth, when he began to blow.

"Now," he continued, "if you work the bellows, you will see that the smoke will be drawn in through the valve, and then will come out through the nose."

This experiment succeeded perfectly well, only just in the midst of the interest that they felt, in seeing the smoke come pouring out through the nose, they heard a bell ring at the house. They knew at once that this bell was for Rollo and Nathan; and so the two boys jumped up from the hearth, and ran out to see what was wanted. They went through the shed into the barn, and thence on till they came to the great barn door, where they had come in. There Rollo stopped,—for he did not like to go out into the snow,—and asked Dorothy,